Optical signals can be routed within optical networks on the basis of the wavelength of those optical signals using wavelength division multiplexing (WDM) and frequency routing techniques. The capacity of an optical network based on such routing techniques is limited, however, by the tuning bandwidth of the lasers in the optical network. The problem of limited capacity can be overcome, and greater system design flexibility achieved, by providing the ability to change the wavelength of a given optical data signal.
Optical devices known as "wavelength shifters" or "wavelength converters" change the wavelength of an optical data signal. Such devices typically operate to transfer data from an optical signal at a first wavelength to an optical signal at a second, desired wavelength.
Prior wavelength shifters performed electro-optical conversions to shift the wavelength of an optical data signal. More specifically, these wavelength shifters converted an optical data signal at a first wavelength into an electrical data signal, then reconverted the electrical signal to an optical signal at the desired wavelength. Such wavelength shifters, however, required complex control circuitry to perform the necessary optical/electrical conversions. Other wavelength shifters utilized Fabry-Perot (multi-pass) amplifiers to transfer data from an optical signal at a first wavelength to an optical signal at a second, desired wavelength. However, Fabry-Perot devices are relatively slow, provide a low contrast ratio between the input and output optical signals, and are not fully tunable within the bandwidth of interest.